In a Long Term Evolution (LTE) system and an improved LTE-Advance system, a downlink physical layer control signalling includes Downlink Grant (DL Grant) information related to downlink transmission required by a terminal (e.g., User Equipment (UE) and Uplink Grant (UL Grant) information related to uplink transmission required by the terminal, so as to indicate various kinds of information such as transmission resource location and modulation and encoding scheme or the like. The physical layer control signalling is transmitted over a Physical Downlink Control Channel (PDCCH). The physical layer control signalling mainly refers to a user-specific control signalling in a physical layer.
In Release (R) 8/9 of the LTE system and R10 of the LTE-Advance system, a physical layer control channel over which the physical layer control signalling is transmitted is generally configured in the first N Orthogonal Frequency Division Multiplexing (OFDM) symbols, and a resource region constituted by the N symbols is generally referred to as a control signalling transmission region.
Available transmission resources of the existing control signalling transmission region (a first control signalling transmission region, or referred to as a first control signalling region) are divided into multiple Control Channel Elements (CCEs), each being a resource unit. The resources occupied by the control signalling are assigned in the unit of the CCE. As a resource unit, the CCE may be subdivided into Resource Element Groups (REGs). A single CCE is constituted by multiple non-consecutive REGs. Generally, 9 REGs constitute one CCE, and each REG is constituted by multiple basic resource elements.
Private control signalling and public control signalling are transmitted in resource unit of the CCE, then mapped to the corresponding REG resources, and then mapped to Resource Elements (RE, which is the minimum resource unit) of multiple Physical Resource Pairs (PRB pairs, also referred to as PRBs for short).
The terminal generally performs blind detection in the following way: initial positions of the private control signalling and the public control signalling are calculated, wherein the private control signalling is often mainly concerned. The Aggregation Level (AL) of the blind detection and the number of the blind detections are as shown in Table 1.
TABLE 1Blind detection space Sk(L)ControlAggregationSize of blind detectionNumber of blindsignaling typelevel Lspace [in CCEs]detections M(L)UE-specific166 (6/1) 2126 (12/2)482 (8/4) 8162 (16/8)Common4164 (16/4)8162 (16/8)
It can be seen from Table 1 that the transmission resources of the control signalling assigned to the user are non-consecutive, which brings many difficulties to the implementation of a closed-loop pre-coding technology in a multi-antenna system, and results in that it is possible to use a diversity technology but difficult to use the closed-loop pre-coding technology for the control signalling region.
In the release after R10, in order to improve the transmission capacity of the control channel to enable the control signalling to support more users, a new control channel region (a second control signalling transmission region, a second control signalling region) is developed, and the control signalling transmission resources for a single terminal may be consecutive time-frequency resources to support the closed-loop pre-coding technology, which improves the transmission performance of the control signalling.
The control signalling regions of the new and old releases are shown in FIG. 1. Some of the transmission resources in a Physical Downlink Shared Channel (PDSCH) transmission region in the original R8/R9/R10 may be allocated for a new control signalling transmission region, so that the transmission of the control signalling supports the closed-loop pre-coding technology, and the improvement of the control signalling capacity makes it possible to support the control signalling of more users. The control channel transmitted in the second control signalling region is referred to as the second control channel or enhanced PDCCH (ePDCCH).
The ePDCCH detection method will be introduced below in terms of resource granularity, ePDCCH candidates pilot port, transmission manner or the like.
In general, a base station first notifies the terminal of an ePDCCH resource set. The base station and the terminal may also appoint a basic resource allocation unit, and then may appoint the sizes of several occupied resources (generally the aggregation of one or more resource application units). The aggregation of N resource application units is referred to as aggregation level N. Generally, one basic resource unit enhanced CCE is defined. The eCCE has a function similar to the CCE. In the second control region, the eCCE may use the definition of the CCE or may modify the definition slightly, or may also make a new definition. The size of the eCCE may be fixed or variable. The eCCE may include a Distributed eCCE (D-eCCE) and a Localized eCCE (L-eCCE) as shown in FIGS. 2 and 3.
The control signalling may define different aggregation levels based on the eCCE, for example, the aggregation level set corresponding to the Localized transmission is {1, 2, 4, 8} or {1, 2, 4, 8, 16}, and different aggregation levels represent different resource sizes. The aggregation level set corresponding to the Distributed transmission is {1, 2, 4, 8, 16} or {1, 2, 4, 8, 16, 32}, and therefore the terminal can perform blind detection on the corresponding aggregation level pointedly.
At present, available aggregation level sets for detection may be determined according to some specific situations, as shown in Table 2 or Table 3.
TABLE 2NECCEusing normal subframes and specialsubframes configuration 3, 4, 8 in normalcyclic prefix subframes, with the numberof REs available for ePDCCH in PRB pairmeeting nEPDCCH < 104All other casesDistributedLocalizedDistributedLocalized transmissiontransmissiontransmissiontransmission221144228844—16—8
TABLE 3NECCENormal subframes and special subframes,configuration 3, 4, 8, withn nEPDCCH < 104and using normal cyclic prefixAll other casesDistributedLocalizedDistributedLocalized transmissiontransmissiontransmissiontransmission22114422884416 1688—32—16
The base station may configure multiple ePDCCH resource sets for the terminal, each ePDCCH resource set may uniquely correspond to a type of Localized transmission (referred to as type L for short) or a type of Distributed transmission (referred to as type D for short). The type of the ePDCCH resource set and the type of the ePDCCH transmission mean the same thing. The types of the ePDCCH resource sets and the types of the ePDCCH transmissions may be Localized or Distributed. The type refers to: if it is configured to be the distributed type, only the distributed ePDCCH is transmitted or detected within the ePDCCH resource set; if it is configured to be the localized type, only the Localized ePDCCH is transmitted or detected within the ePDCCH resource set.
For example: when 3 Resource sets are configured,
The ePDCCH resource set 1 is the Localized type, the terminal detects the ePDCCH resource sets of localized type in a subframe S using a corresponding AL={1, 2, 4, 8};
The ePDCCH resource set 2 is the Distributed type, the terminal detects the ePDCCH resource sets of distributed type in a subframe S using a corresponding AL={1, 2, 4, 8, 16};
The ePDCCH resource set 3 is the Distributed type, the terminal detects the ePDCCH resource sets of distributed type in a subframe S using a corresponding AL={1, 2, 4, 8, 16}.
The AL corresponding to the case of Localized type is aggregated according to the localized eCCE, the AL corresponding to the case of Distributed type is aggregated according to the Distributed eCCE.
To sum up, the number of blind detections is increased greatly when more resource sets are configured, which limits the configuration number of the resource sets. In addition, in a case where the total number of blind detections is constant, the number of blind detections of each AL in each ePDCCH resource set is small, which results in that the effect of configuring multiple ePDCCH resource sets cannot be exploited, causing ePDCCH performance loss.